1. Field of the Invention
The present invention relates to optical gyros for detecting rotation and, more particularly, to optical gyros of the ring laser type.
2. Related Background Art
The conventionally well-known gyros for detecting the angular velocity of a moving object include mechanical gyros having a rotor and an oscillator, and optical gyros. In particular the optical gyros have the feasibility of instantaneous activation and wide dynamic ranges and thus are bringing about innovation in the technical fields of gyros. The optical gyros embrace ring laser gyros, optical fiber gyros, passive ring resonator gyros, and so on. Among these, the pioneer gyros were the ring laser gyros using gas lasers, which have already been used in practice, e.g., in airplanes. Semiconductor laser gyros as integrated on a semiconductor substrate have been also proposed recently as compact, highly accurate ring laser gyros; for example, as described in Japanese Patent Application Laid-Open No. 5-288556.
There is also a technique of letting a clockwise laser beam and a counterclockwise laser beam travel in a semiconductor ring laser and detecting the angular velocity by making use of the difference between frequencies of the two laser beams (e.g., as described in Japanese Patent Application Laid-Open No. 57-43486 or U.S. Pat. No. 4,431,308).
Specifically, the angular velocity is determined from a change in the frequency (beat signal) of terminal voltage of the laser element.
However, the laser element is sensitive to noise included in the driving source and external environment and involved the problem that the beat signal was unstable at a standstill.
It is thus an object of the present invention to provide ring laser gyros that can detect the beat signal accurately and stably.
For accomplishing the above object, a gyro according to the present invention comprises a ring laser in which laser beams of different oscillation frequencies coexist and propagate in mutually opposite circulation directions in an optical resonator, a power source of driving for the ring laser, a device for measuring a difference between the oscillation frequencies of the laser beams, and a device for controlling the power source of driving according to the frequency difference.
The foregoing ring laser is, for example, a ring laser provided with an optical waveguide having an asymmetric taper shape. The control of the power source of driving is performed so that a beat signal detected from the ring laser becomes constant.
Another gyro according to the present invention is a gyro comprising a semiconductor ring laser permitting detection of a beat signal at a standstill, the gyro further comprising a power source of driving and a control device for effecting feedback control on the power source of driving for the semiconductor ring laser so that the beat signal at a standstill becomes stable.
Another gyro according to the present invention is a gyro comprising a semiconductor ring laser permitting detection of a beat signal at a standstill, wherein feedback control is effected on a power source of driving so as to cancel out a change in the beat signal due to rotation of the gyro and wherein an angular velocity is detected from a feedback signal used in the feedback control.